Just trying to push the limits of Swift to see what's possible. Trying to get an overall understanding of how code can be structured. Especially around object life cycles. Check the revisions for iterations over the design. Please don't write code like this, unless you know what you are doing.

Avatar.swift

struct Imager
{
    unowned let session: Session
    unowned let avatar: Avatar
    
    func image(imageView: UIImageView) {
        
        let download = self.session.download(self.avatar.image) { [weak imageView = imageView] (data, response, _) in
            
            guard let _imageView = imageView else {
                return
            }
            
            dispatch_async(dispatch_get_main_queue()) {
                _imageView.image = UIImage(data: data!)
            }
        }
        
        download.resume()
        
        imageView.image = UIImage(named: self.avatar.defaultImage)
    }
}

class Avatar {
    let defaultImage = "avatar"
    let image: String
    
    init(image: String) {
        self.image = image
    }
    
    lazy var imager: (session: Session) -> Imager = {
        return { [unowned self] (session: Session) in
            return Imager(session: session, avatar: self)
        }
    }()
}